Driveshaft compatibility 40 hp merc 402 1975 to 1979

[neller]

I recently bought a 1975 merc 40 402 since my 1979 merc 40 402 lost compression in the upper cylinder. I got the new motor (1975) running, went to put my jet end on and can't get the driveshaft splines to line up. Both driveshafts have 11 splines and seem to be 3/4 of an inch in diameter, although I can't exchange the lower units between the motors.

The top of the shafts look visibly different with the shaft from 1975 having a tapered end with a pin on top, wheras the shaft on the 1979 is squared off without a pin.

Any ideas on whether the drive shafts are that different? Is there some sort of adaptor? Do I need to have the shaft removed from the lower unit and replaced in the jet end to get it on the motor?

Thanks,

Pat

 

[neller]

Re: Driveshaft compatibility 40 hp merc 402 1975 to 1979

Would it help if I posted some pictures of the two driveshafts? Did driveshafts change between 1975 and 1979?

Thanks,

Pat